With the spread of distributed power sources such as photovoltaic cells (PVs), fuel cells, and so on, various methods for obtaining optimal power from such power sources are being developed.
In the case where PVs are used as a distributed power source, there is a method that provides a DC/DC converter that carries out MPPT (Maximum Power Point Tracking) control in each PV in order to obtain a maximum amount of power from the PVs.
Japanese Translation of PCT International Application Publication No. 2010-521720, for example, discloses a DC/DC converter that carries out MPPT control being provided with a communication function, and information obtained from current and voltage sensors and the like is sent to a central analysis station, where the information is monitored, controlled, and analyzed.
Furthermore, Japanese Patent Application Laid-Open Publication No. 2012-004626, for example, discloses transmitters provided in each of a plurality of PVs transmitting power generation information to a communication parent device over a power line in order to monitor power generated by the PVs.
In this manner, the concept of providing a communication device in each PV has been explored, but such a configuration also means separately providing a host apparatus for the plurality of PVs, which increases the cost of the overall system by the amount of the host apparatus. Furthermore, although the host apparatus is described as carrying out control, the stated documents do not describe exactly how that control is carried out.
Meanwhile, there are cases where a plurality of strings, in each of which a plurality of PVs are connected in series, are connected in parallel, and are further connected to a PCS (Power Conditioning System) and used. A PCS converts a DC (Direct Current) output from the PVs into a household-use AC (Alternating Current) output, and output voltages of the respective strings connected in parallel are adjusted to the same value. Here, in the case where the number of PVs connected in series differs from string to string, the output voltage is adjusted for each PV in each string. Such adjustment is thus carried out not only when a photovoltaic power generating system is installed, but also in a case such as where a PV panel or panels have partially failed, and there are no systems that carry out the adjustment autonomously.